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Equipment Description

2-1. AN/TTC-39( )(V)

The Automatic Telephone Central Office AN/TTC-39( )(V) is a mobile, automatic, modular, electronic circuit switch. It operates under processor control with integral COMSEC and multiplex equipment. The AN/TTC-39 switches secure and nonsecure voice and data traffic. It is compatible with the Defense Communications System AUTOVON and with the tactical communications systems of the armed services. It can also operate with the NATO Integrated Communications System and with Allied organic combat communications systems. The circuit switch can transit from the present analog system to the mostly secure digital system of the future by replacing analog matrices with digital ones and with associated multiplex equipment for digital transmission groups (DTG). The switch will soon be modified to become the Automatic Nodal Control Circuit Switch AN/TTC-39A( )(V).

2-2. Overview

The AN/TTC-39 is in two sizes of configurations, single shelter and dual shelter. The descriptions following are for both of these. The part numbers and reference designations used are from TM 11-5805-681-12. Figures 2-1 and 2-2 show the AN/TTC-39 and the equipments used with it for both the single shelter (300-line) and dual shelter (600-line) installations. These figures show the switch in the transportation mode. Table 2-1 lists the items making up the equipments shown in Figures 2-1 and 2-2. Table 2-2 lists the items supplied or used with the switch. This table gives the common name and the official nomenclature of each item.


Table 2-3 identifies the current switch configurations that have received official nomenclatures. The AN/TTC-39(V)2 (dual shelter switch) and the AN/TTC-39(V)3 (single shelter switch) are the two basic configurations you will most often see in the field. The AN/TTC-39(V)4 and the AN/TTC-39(V)5 are 400-Hz powered versions of the two basic configurations. The switch is modular in both software and hardware. Various versions of the basic configurations can be obtained by changing the mix of analog and digital matrices in the switch. Table 2-4 shows some possible configurations and their terminal capacities. Note that the specific terminations vary from the nominal sizes.


Figure 2-3 shows the roadside and curbside elevations for the single shelter switch. Figure 2-4 shows this for the dual shelter switch. Labels and keys identify the equipments. These key letters will appear in later tables and figures. Figure 2-5 is a functional block diagram, which the following text describes. Follow the diagram for each part of the description.

Power group. A prime AC power source pro-vides power to the shelter. This can come from engine generators or from commercial power. A backup power subsystem (batteries) provides 15 minutes worth of power to critical AC and DC operating equipment.

Central processor group (CPG). This group of equipments processes, routes, and controls the calls in the circuit switch. Redundant central processor units (CPU) increase reliability and prevent downtime. Interface devices provide operator and maintainer access to the CPG. Each switch has two magnetic tape transports (MTT). A magnetic tape controller (MTC) located in an interface control unit controls the MTTs.

Common equipment group (CEG). This group handles the control, switching supervision, and signaling of analog and digital lines and trunks. A common equipment distribution frame (CEDF) interconnects conference bridge units (CBU), senders, receivers, scanners, and control and timing equipments.

COMSEC common equipment facility (CEF). The CEF incorporates the racks that contain all the trunk and line encryption equipment of the switch. This includes automatic key distribution centers, key generators, trunk encryption devices, loop key generators (LKG), and the necessary interface units.

Space division switching group (SDSG). The SDSG includes a space division matrix (SDMX), analog scanners, line termination units (LTU), and type II modems. Each group provides circuit switching functions for up to 120 terminations of analog voice and data lines and trunks.

Time division switching group (TDSG). This group includes a time division matrix (TDMX); various loop, group, and supergroup multiplex/demultiplex (MUX/DEMUX) and modems; scanners and signaling buffers; and associated equipment. It provides digital circuit switching functions and interface connections to digital voice and data lines and trunks and to selected analog subscribers. It also provides external terminations for digital loops, 4-wire analog AC supervised loops, and transmission groups. Each TDSG can terminate a maximum of 150 circuits.

Special circuits group (SPCG). The SPCG includes an auxiliary patch panel, various adapters (SF, E&M, DC closure), timing distribution, line driver interface, and a circuit switch summary alarm.

Operator machine interface group. This group enables operator personnel to interact with the switching equipment and to communicate with other shelters, switches, control activities, and subscribers.

  • Call service position (CSP). The CSP assists subscribers who are having difficulties or are not equipped to make certain calls.
  • Control and alarm panel/control transfer logic (CAP/CTL). The panel displays circuit summary system status configuration and the status of the redundant processors. The CTL portion lets a user select the processor, controller, and peripheral configuration by hand.
  • Video display unit/keyboard (VDU/KB). This unit is the main interface between the operator and the CPG. It consists of a video display monitor, a keyboard, and a video display controller.
  • Digital subscriber voice terminal (DSVT). The DSVT provides the switch operator with a secure means of communications to other switches or to subscriber terminals. It also provides secure telephone communications between shelters.
  • Intercommunication Station LS-147/FI. This intercom system provides local communication between the circuit switch shelters and any colocated message switch shelter.
  • Teletypewriter (TTY) communications terminal. A TTY (AN/UGC-74A) resides in each shelter. It consists of a keyboard for data entry and a page printer for hard copy. Both the operator and the maintainer may use it.


The AN/TTC-39 may be shipped by fixed-wing cargo aircraft, military helicopters, M series military cargo vehicles, rail, sealift, and demountable transporters. It meets the following storage and transfer environmental conditions:

  • Temperature: -70 F to +160 F, (magnetic tape cassettes: -40 F to +140 F).
  • Relative humidity: 100 percent up to +80 F, dew point 86 percent at +l00 F; 5 percent at +120 F.
  • Altitude: Sea level to 12,192 meters (40,000 feet).
  • Sand and dust: Wind speeds up to 35 knots (40 miles per hour).
  • Snow: 18.26 kilograms per square centimeter (40 pounds per square inch) loading.
  • Fording: No leakage when immersed up to 53.34 centimeters (21 inches).
  • Salt fog: Capable of prolonged exposure.
  • Fungus: Resistant.
  • Vibration: Roads, cross-country terrain, water, and fixed-and rotary-wing aircraft.
  • Shock: Transport by rail, water, and air.
  • Orientation: In any position for a period of 2 years.

Power and environmental control system. (See Figure 2-2.)

Prime power comes from an electric power plant (AN/MJQ-10 for single shelter or AN/MJQ-12 for dual shelter installation). External power to each shelter connects to a power entry panel (PEP) on the exterior wall. A master power distribution unit feeds prime input power to one of two waterproof receptacles on the PEP. The master power distribution unit (ON-224T) accepts a source of 50/60-Hz power from a commercial power line or a military electric power plant (AN/MJQ-10 or AN/MJQ-12). The power distribution unit monitors, controls, and distributes power from up to four sources to up to four shelters. The unit also contains circuits to monitor phase relationships of the applied AC power. The environmental control units (ECU) mounted on each shelter provide either warm or cool air. Shelters operating at 400-Hz ((V)4) require a different ECU than that for 50/60-Hz ((V)1,2,3). Shelters using 400-Hz power use an additional DC/AC converter.

2-3. Hardware

Table 2-5 lists the AN/TTC-39 hardware items by group, by function, and by nomenclature. Figures 2-6, 2-7, and 2-8 show the locations of the equipments listed in Table 2-5. The equipments are described in the subparagraphs below. Key designations (in parentheses below) are from Table 2-5 and Figures 2-6, 2-7, and 2-8. Note that not all the keys in the table are shown in the diagrams.

Analog switching.

Analog subscribers connect to the SDMX (E3) through the signal entry panel (SEP) (E2), the SDSG patch panel (El), and the LTU (E4). Subscribers using SF, DC, or E&M signaling also go through the auxiliary special circuits patch panel (M1) or the patch and control panel (K2). The patch panels enable special adapters to be inserted in series. These adapters are in line with the LTUs on the first cable of each analog rack. If the terminations are used without the adapters, the adapters must be patched out.

Line termination units. LTUs convert signals to a standard used by the SDMX (E3). The special adapters make signals compatible with these normal wideband LTUs.

Space division matrix. Analog subscribers from the SDMX connect to digital subscribers via intermatrix units that are part of the SDSG.

Conference bridge unit. A subscriber can set up a five-party analog or digital conference with a CBU (K5). Use more than one bridge to set up larger conferences. A conference can be either nonsecure or secure if the appropriate security devices are used. A conference can also be progressive (caller initiated) or preprogrammed.

Receiver matrix unit (RMU). The RMU (K4) provides a switched analog path for up to 60 analog subscribers terminated on the TDMX (digital side of the switch) to five dual tone multifrequency (DTMF) receivers (K6). The switch can thus receive address signals from these subscribers. Three digital racks are needed to reach this maximum of 60. These analog subscribers are grouped 24 to the first digital rack, 24 to the second, and 12 to the third.

Matrix controller (MXC). The MXC (K13) in the switching controller group (SCG) controls the RMU.

Special circuits group. The special circuits group in the 300-line switch (M) can accommodate twenty-four 4-wire adapters or sixteen 6-wire adapters. The 600-line switch can accommodate thirty-six 4-wire adapters or twenty-four 6-wire adapters. With these, the SDSG can connect to single frequency (SF) 2600-Hz, DC closure, and 6-wire loops or trunks.

Circuit switch summary alarm. The circuit switch summary alarm (M2) is on the auxiliary special circuits patch panel (Ml). Also on the patch panel are normal-through jacks for lines or trunks using the special adapters.

Digital switching.

Traffic and transmission lines enter the digital system through the SEP (D4) and the TDSG patch panel (D1). Analog traffic then goes through a continuously variable slope delta (CVSD) modulator (D2). The digital subscriber loop goes through a diphase loop modem A (DILPA) (D12). Digital transmission groups pass through modems (D5). From these points, the digital traffic then goes through various MUX/DEMUX, patch panels, buffers and interface units via a switch multiplexer/demultiplexer (SMD) (D6) to the TDMX (D3).

Switch multiplexer. The switch multiplexer processes calls into 64-channel data streams. The TDMX (D3) performs the digital switching of these subscribers. The central processor controls the matrix through the matrix controller (K13). This resides in the switching controller group (SCG) of the CEG (K).

Switch multiplexer/demultiplexer. The SMD (D6) combines sixty-four 32-kHz digital data streams into a 64-channel, 2.048-MHz multiplexed data stream, and vice versa.

Digital and analog scanners. A digital scanner (D7) searches all switched digital loops, groups and trunks. An analog scanner searches those TDMX loops that are terminated on analog telephones. (A maximum of 60 subscribers off the TDMX may be analog. Refer back to paragraph 2-2a(4).) These scanners determine the change of status of each external termination (on-hook or off-hook). This change of status is then forwarded to the processor through the scanner controller (K14).

Remote special devices demultiplexer. The remote special devices demultiplexer (D8) decodes addresses from the special devices controller (K15) and sends out commands to the group modems (D5). It also feeds signals to the transmission group module (D9) and the SMD (D6) and sends resets to the loop MUX/ DEMUX (D10) and remote fault multiplexer (D11).

Remote fault multiplexer. The remote fault multiplexer (D11) connects to all monitored equipment in the TDSG. It sends fault information to the fault controller (K16) in the SCG.

Diphase loop modem A. The DILPA (D12) handles conditioned diphase signals between individual subscribers and the time division portion of the switch. It also provides DC power to connected DSVTs.

Continuously variable slope delta. The CVSD modulator (K7) translates analog signals to digital signals and vice versa. This enables the switch to terminate 4W DTMF AC supervised analog telephones. The CVSD modulator card (K7) in the common equipment group is used in conjunction with the local call service position (LCSP) when terminated on the TDMX. The diphase loop modem A located in the CEG is used to terminate the signaling part of the LCSP on the TDMX. Termination of the LCSP on the TDSG or SDSG is determined by the CEDF patching.

Group and supergroup modems. Diphase supergroup modems (D15), diphase group modems (D13), and dipulse group modems (D14) terminate transmission groups brought into the circuit switch over CX-11230/G coaxial cables. The diphase group and supergroup modems are used to interface with the new family of digital group multiplex transmission equipments in groups as follows:

  • Group modems - 8, 9, 16, 18, 32, 36, 48, 64, 72.
  • Supergroup modems - 128, 144.

The dipulse group modem is used to interface with existing multichannel equipment (TD-754, TD-204, TD-660, AN/GRC-143, and AN/GRC-144).

Diphase supergroup modems. Diphase supergroup modems (D15) connect 128 and 144 channel supergroups to the switch.

Digital in-band trunk signaling buffer (DSB). The DSB (D16) provides in-band signaling and supervision between the AN/TTC-39 and a digital subordinate switch such as the SB-3865.

Trunk signaling buffer (TSB). The TSB (D17) provides common channeling signaling (CCS) on interswitch trunk groups. It performs the required encoding, decoding, data storage, and message formatting. TSBs are used in conjunction with type II modems for analog interswitch trunks.

Transmission group module. The transmission group module (D9) contains a group buffer, a group framing unit, and output control logic. These units work with the trunk encryption device (TSEC/KG-81) (J4) to adjust, encrypt, decrypt, and frame synchronize DTG data.

Remote signaling buffer controller (SBC) multiplexer/demultiplexer (RSBMD). The RSBMD (D18) transfers input and output data between the TSB (D17), the digital in-band trunk signaling buffer (D16), and the SBC (K12).

Group multiplexer and demultiplexer. The group multiplexer and demultiplexer (D19) consists of 16 nine channel multiplexer/demultiplexer (NCMD) units. From these, digital groups can be formed in modularities of 8,9,16,18,32,36,48,64, 72,128, and 144.

Digital signal generator. The digital signal generator (K8) provides code words, recorded announcements, and digitized tones to both digital and analog subscribers. A CVSD voice digitizer converts digital signals to analog waveforms.

Digital receiver. A digital receiver (K9) picks up address signals from calling subscribers. It then decodes the signals and sends them to the processor for action. The processor assigns the call to the digital receiver.

Essential user bypass. If both local processors fail, the essential user bypass (EUB) selector (if programmed and activated) routes selected digital subscribers to a distant switch. It can handle up to 60 such subscribers.

Control and timing equipments.

These equipments reside in the CEG (K). They provide for switching, supervision and signaling of analog and digital loops and trunks. Overall switch control is the function of the CPG. Exercise of control is through the SCG, the signaling buffer controller (K12), and the COMSEC controller (K11). The master timing generator (MTG) (K1) and local timing generators (LTG) provide system timing. The CAP/CTL (C) provides configuration control and system fault display.

Switching controller group. The SCG is in the CEG (K). It includes the scanner, receiver, sender, special devices, fault matrix, test generator, and CPU central controllers. Each device controller connects to a specific set of devices. Access to the CPG is through the CPU central controller. The controllers access the following devices:

  • Scanner -- analog, DC, and digital scanners.
  • Receiver -- DTMF, multifrequency, digital, and auxiliary receivers.
  • Fault -- all devices in the system.
  • Sender -- sender devices.
  • Special devices -- miscellaneous devices.
  • Matrix -- time division and space division matrices.
  • Test generator -- loop testing through other controllers.

COMSEC controller. The COMSEC controller (K11) provides bidirectional serial parallel data conversions for interface with the CEF.

Master timing generator. The master timing generator (K1) provides all the clock signals required by the switch. It can generate these signals itself, or the recovered clock can synchronize them from the received clock patch panel.

Central processor group.

This group is the brain of the circuit switch. It is the link between the software and hardware. It stores programs and it controls the switch functions of call processing, switch control, and fault detection. Of the two processors, only one actively processes traffic. The other is redundant. The CPU (L1) provides the logic and computational ability to compose and interpret data, to assess status, to search tables, and to perform arithmetical functions. The interface control unit (L5) provides an interface between processors. It also provides access to both the magnetic tape transports (L6) and the TTYs (F). The switch stores programs both in core memory and on tape.

Operator machine interface.

The operator and maintainer access the switch through a VDU/KB (H), a TTY (AN/UGC-74A (F)), the LCSP (I1), the remote call service position (RCSP), a remote control switchboard (C-10333/TTC-39(V)) (I2), an intercommunications station (LS-147/FI) (B), and the control and alarm panel/control transfer logic (C) already described. The VDU/KB connects the operator to the processor. It updates the data base, reports system status, and exercises special maintenance routines. The TTY includes a keyboard and page printer, It serves as a backup for the VDU/KB and provides a hard copy of processor messages. Intercom stations in each shelter of the circuit switch and connections to intercoms in the local AN/TYC-39 message switch shelter provide convenient local switch communications. The switch operator helps complete local calls, supplies directing and routing information, receives trouble reports, verifies busy and no answer calls, and sets up progressive conference calls. The operator also handles verbal precedence and preemption requests, holds and splits calls, and places secure calls through the LCSPs or RCSPs.

2-4. Communications Security Group

COMSEC equipment is both physically and electrically integrated into the AN/TTC-39 circuit switch. The AN/TTC-39 serves both secure and nonsecure analog and digital users. Thus its system security features must be able to provide a mixture of secure and nonsecure communications. The COMSEC equipment described below performs these functions. The key letters in parentheses are from Table 2-5. In the AN/TTC-39, built-in equipment and terminal devices provide the basis for end-to-end encryption. FM 24-27A describes the encryption/decryption capability in more detail.

COMSEC common equipment facility.

The CEFs identified in Figures 2-6, 2-7, and 2-8 as (J) are an integral part of the AN/TTC-39. They are equipment racks that house the plug-in COMSEC equipment needed to establish and maintain the requisite security for calls and trunk traffic flow. In the 300-line single shelter switch, the COMSEC CEF (J1) is the HGF-85/TSEC. In the control shelter of the 600-line switch the CEF (J2) is the HGF-82. A small trunk encryption module (J9) in the switching shelter of the 600-line switch provides added trunk encryption devices. The CEF is the equipment rack that contains the trunk security devices required to encrypt and decrypt all DTG traffic. There are also loop security devices to encrypt and decrypt all loop traffic. Interface units provide access to the communication and computer equipment of the switch. The circuit switch uses the following items of COMSEC equipment:

  • The TSEC/ KG-82, loop key generator (J5) is a loop security device. It encrypts and decrypts signaling and digital traffic received from a digital subscriber. It also provides the encryption interface for the circuit switch to the AN/TYC-39 trunks.
  • The TSEC/KG-81 or KG-94 trunk encryption device (J4) encrypts and decrypts trunk traffic.
  • The TSEC/KG-83 key generator (J6) generates electronic keys.
  • The HGX-83/TSEC automatic key distribution center (J7) stores and distributes keys.
  • The HGX-84/TSEC interface control unit (J8) provides the electrical interface between the security devices and the central processing unit of the switch.
  • The HGX-82/TSEC loop key generator common unit (J3) serves as the equipment control unit for up to eight KG-82s.

Terminal security device.

The AN/TTC-39 connects to the following terminal COMSEC devices:

  • KY-68 digital subscriber voice terminal performs the audio processing, signaling, and cryptographic functions needed to provide secure and nonsecure access to the AN/TTC-39.
  • KY-90 secure digital net radio interface unit provides semiautomatic connection between VINSON secured radios and switched subscribers via the AN/TTC-39. PARKHILL and ANDVT nets can also be connected if COMSEC equipment is collocated with the KY-90.
  • KG-84/84A dedicated loop encryption device connects with the KG-82 in the switch to provide secure loops to data terminals and secure trunks to the AN/TYC-39.

2-5. Software

The operational software in the AN/TTC-39 consists of independent modules operating under control of an executive program. The software operates in real time. Thus it must be driven by external events. Since these events happen randomly, queue processing is an essential part of software design. The operating program queues the event for service and processes it in turn. It then notifies the program that requested the service that the service is completed. Table 2-6 describes the software features of the switch. It includes the title and mnemonic of each program module and tells what the module does. Some important operating features and processes are listed below:

On-line control and operational program (OLCOP).

The OLCOP is the primary on-line software operating system. It initiates program activity and schedules the programs listed in Table 2-6. It services interrupts and generally provides traffic control.

Cold start.

A system cold start initializes the switch to an off-line state. The supervisor mounts the operational program tape (program library tape). A reset command then initializes each device in the system. It also initializes all buffer control tables. The system accepts the time of day as an input parameter. It sends a message to the operator on the visual display unit (VDU) when the start-up process is completed.


This is a process that takes place during processor switchover. It ensures that no through-connected calls are lost.

CAP/CTL monitoring.

The operating system reads the CAP/CTL and determines if the configuration has changed. It compares the current CAP/CTL map to the previous one. The system processes the necessary changes.

Input/Output (I/O) software.

Centralized I/O software receives I/O requests from the application programs. It then generates the necessary I/O commands and services interrupts from the hardware. Priority levels determine which requests will be serviced first. Scanning, receiving, and trunk signaling channel inputs are examples of high priority interrupts. I/O handlers access each of the controllers in the switch control group. These include the signaling buffer controller, the COMSEC controller, the magnetic tape controller, the VDU/KB controller, the TTY controller, and the CAP/CTL.


Software diagnostics may be either core or tape-resident. They may be run in on-line or off-line and may be operator-initiated or run on a continuous basis. (See paragraph 3-15.)


The main program operates on a major/minor cycle time base to provide external event interrupt processing. Figure 2-9 illustrates the modules included in these cycles. Each of these modules is illustrated with its mnemonic program name. The flow shown in the diagram indicates the sequence of program operation. Interrupt handlers service hardware interrupts. Priorities determine which are handled first. Scanning inputs, receiving inputs, and trunk signaling inputs are high priority interrupts. They must be serviced quickly. VDU input is an example of a low priority interrupt.

2-6. AN/TTC-39A

The modifications to the AN/TTC-39 which turn it into a AN/TTC-39A are in these major areas:

  • The processor L3050 is replaced by the L3212A. This new one has 512K of memory and is 19 percent faster. There is a redundant processor as before. It is also smaller and uses less power.
  • Internal and external digital connections are increased.
  • Certain control functions have been added.
  • Certain switch functions are more easily done.

  • The analog/digital matrix configuration is standardized.
  • The ability to condition up to 24 analog circuits is provided. Descriptions of some of these changes follow. Chapter 3 covers the functional changes.


The changes to the switch have increased its capacity above that of both the 300-line and 600-line AN/TTC-39s. This capacity resides in a single shelter, eliminating the need for a dual shelter switch. All AN/TTC-39As will initially have one analog matrix (or switching group) and two digital matrices (or switching groups). Figure 2-10 shows the internal arrangement of the AN/TTC-39A. If you compare this figure with Figure 2-3, you will see very little change on the roadside. The curbside however is completely changed.


A new atomic timing standard is added. Rubidium is used to provide improved clock reference.

Switching group.

The TDSG in the AN/TTC-39 is replaced by a time division switching group modified (TDSGM). The TDSGM memory structure and switching are functionally the same as the old TDSG. However, the TDSGM has twice the capacity. It has 15 DTGs, giving a switch total of 30 DTGs (using 2 TDSGM).

Communications security.

The major change for COMSEC equipment is that there are 15 KG-94 trunk encryption devices. These replace the 6 KG-81s. There are also 32 KG-82 loop key generators.


Digital voice orderwire (DVOW) and analog voice orderwire (AVOW) capabilities are added. Diphase DTGs are used with the DVOW, and diphase and dipulse DTGs are used with the AVOW. The KY-57 (VINSON) is provided for the DVOW. There are 12 DVOWs and 6 AVOWs available simultaneously. These are available to all DTGs and analog trunks by patching. Both types are controlled through the orderwire control unit II.

Remote video display unit.

A remote VDU position is added to allow an external attendant to perform the same functions as at the internal position. A remote VDU controller is also added.

Low speed cable driver modem.

Two low speed cable driver modems (LSCDM) are added. These are for dedicated operation on DTGs 15 and 30.

Use of fiber optics.

Fiber optic transmission cables are used both internally and externally to replace metallic paths.

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